Xcode 8 Objective-C category warning

Question

I\'m using Xcode 8 and Swift 3.0. What does this error message mean?

ld: warning: Some object files have incompatible Objective-C category definition

Answer 1

This warning appeared in my project after adding a framework that used Objective-C in my application that otherwise used Swift 3 entirely.

By declaring all static functions and static variables in all extensions as @nonobjc this warning went away.

For example

extension Notification.Name {
    @nonobjc static let MyNotificationName = Notification.Name("NNSongFavoriteStatusDidChangeNotification")
}

or

extension UIColor {
    @nonobjc static let superGiantRed = UIColor(red: 180.0/255.0, green: 40.0/255.0, blue: 27.0/255.0, alpha: 1.0)
}